Boost属性树：从节点中删除属性 [英] Boost Property Tree: Remove attribute from a node

问题描述

我有以下XML文件：

<?xml version="1.0" encoding="utf-8"?>
<gexf>
  <graph>
    <nodes>
      <node id="0" label="0" start="0" end="25"/>
      <node id="1" label="1" start="1"/>
      <node id="2" label="2" start="2"/>
      ...
    </nodes>
    <edges>
      <edge id="0" source="0" target="1" start="7" end="19"/>
      <edge id="1" source="0" target="2" start="8" end="20"/>
      ...
    </edges>
  </graph>
</gexf>

我想删除 start source =0和 target =1的边缘的 end code>。

I want to remove the start and end attributes from the edge with source="0" and target="1".

我试图这样做的方式是在下面的代码。假设XML文件命名为 ptree_test.gexf 我读它，在树中找到正确的边，然后尝试使用擦除以清除属性。

The way I've tried to do this is in the following code. Assuming the XML file is named ptree_test.gexf I read it in, find the correct edge in the tree, and then attempt to use erase to get rid of the attributes.

#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
#include <iostream>

using boost::property_tree::ptree;

int main(int argc, char *argv[]) {

  ptree pt;

  read_xml("ptree_test.gexf", pt);

  // Now find edge (0, 1) and delete the start and end attributes
  ptree edge;
  int id1, id2;
  id1 = 0;
  id2 = 1;

  for(auto &e : pt.get_child("gexf.graph.edges")) {
    int s, t;
    s = e.second.get<int>("<xmlattr>.source");
    t = e.second.get<int>("<xmlattr>.target");

    // Check if this is the correct edge
    // Two checks because it can be reversed
    if((id1 == s && id2 == t) || (id1 == t && id2 == s)) {
      edge = e.second;
      break;
    }
  }

  for(auto & attr : edge.get_child("<xmlattr>")) {
    if(attr.first == "end" || attr.first == "start") {
      edge.erase(attr.first);
    }
  }

  write_xml(std::cout, pt);
  return 0;
}

这不起作用。它不会删除该属性。事实上，如果我输入一个打印 edge.erase（attr.first）的返回值的调试语句，它会显示 0 。

This does not work. It doesn't remove the attribute. In fact, if I put in a debug statement that prints the return of edge.erase(attr.first) it shows 0.

推荐答案

主要的问题是你在这一行中拷贝子树：

The main problem is that you are making a copy of the subtree in this line:

  edge = e.second;

，然后修改 后来，因为@NicolBolas说你需要一个保护者擦除。完整代码如下所示：

and then modifying that copy instead of the original. Later, as @NicolBolas said you need an interator to erase. The full code looks like this:

int main(){
        boost::property_tree::ptree pt;
        read_xml("ptree_test.gexf", pt, boost::property_tree::xml_parser::trim_whitespace);
        int id1, id2;
        id1 = 0;
        id2 = 1;
        for(auto &e : pt.get_child("gexf.graph.edges")) {
            int s, t;
            s = e.second.get<int>("<xmlattr>.source");
            t = e.second.get<int>("<xmlattr>.target");
            // Check if this is the correct edge
            // Two checks because it can be reversed
            if((id1 == s && id2 == t) || (id1 == t && id2 == s)){
                auto &children = e.second.get_child("<xmlattr>");
                for(auto attrIt = children.begin(); attrIt != children.end(); ++attrIt){
                  if(attrIt->first == "end" || attrIt->first == "start")
                    attrIt = children.erase(attrIt);
                }
                break; // maybe shouldn't be here to keep looking?
            }
        }
        write_xml("ptree_test_copy.gexf", pt, std::locale(), bpt::xml_writer_settings<std::string>{'\t', 1});
}

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